Try/catch does not seem to have an effect

Question

I am new to powershell, and I am trying to add error handling via try/catch statements, but they don't seem to actually be catching the error. This is powershell v2 CP3.

$objComputer = $objResult.Properties;
$strComputerName = $objComputer.name
write-host "Checking machine: " $strComputerName

try
{
    $colItems = get-wmiobject -class "Win32_PhysicalMemory" -namespace "root\CIMV2" -computername $strComputerName -Credential $credentials
    foreach ($objItem in $colItems) 
    {
        write-host "Bank Label: " $objItem.BankLabel
        write-host "Capacity: " ($objItem.Capacity / 1024 / 1024)
        write-host "Caption: " $objItem.Caption
        write-host "Creation Class Name: " $objItem.CreationClassName      
        write-host
    }
}
Catch 
{
    write-host "Failed to get data from machine (Error:"  $_.Exception.Message ")"
    write-host
}
finally 
{ }

When it fails to contact a specific machine, I get this in console, and not my clean catch message:

Get-WmiObject : The RPC server is
unavailable. (Exception from HRESULT:
0x800706BA) At Z:\7.0 Intern
Programvare\Powershell\Get memory of
all computers in AD.ps1:25 char:34
+ $colItems = get-wmiobject <<<< -class "Win32_PhysicalMemory"
-namespace "root\CIMV2" -computername $strComputerName -Credential
$credentials
+ CategoryInfo : InvalidOperation: (:) [Get-WmiObject],
COMException
+ FullyQualifiedErrorId : GetWMICOMException,Microsoft.PowerShell.Commands.GetWmiObjectCommand

Answer 1

I don't believe that the try-catch-finally syntax is avaiable in PowerShell?

I think you'll have to implement it yourself, see this blog post on "Technical Adventures of Adam Weigert" (haven't tried this myself). Of course, that might be what you've already done, in which case this answer probably isn't that helpful, sorry.

Example usage (copy/paste from Adam Weigert's blog):

Try {
    echo " ::Do some work..."
    echo " ::Try divide by zero: $(0/0)"
} -Catch {
    echo "  ::Cannot handle the error (will rethrow): $_"
    #throw $_
} -Finally {
    echo " ::Cleanup resources..."
}

Otherwise you'll have to use exception trapping.

Answer 2

I was able to duplicate your result when trying to run a remote WMI query. The exception thrown is not caught by the Try/Catch, nor will a Trap catch it, since it is not a "terminating error". In PowerShell, there are terminating errors and non-terminating errors . It appears that Try/Catch/Finally and Trap only works with terminating errors.

It is logged to the $error automatic variable and you can test for these type of non-terminating errors by looking at the $? automatic variable, which will let you know if the last operation succeeded ($true) or failed ($false).

From the appearance of the error generated, it appears that the error is returned and not wrapped in a catchable exception. Below is a trace of the error generated.

PS C:\scripts\PowerShell> Trace-Command -Name errorrecord  -Expression {Get-WmiObject win32_bios -ComputerName HostThatIsNotThere}  -PSHost
DEBUG: InternalCommand Information: 0 :  Constructor Enter Ctor
Microsoft.PowerShell.Commands.GetWmiObjectCommand: 25857563
DEBUG: InternalCommand Information: 0 :  Constructor Leave Ctor
Microsoft.PowerShell.Commands.GetWmiObjectCommand: 25857563
DEBUG: ErrorRecord Information: 0 :  Constructor Enter Ctor
System.Management.Automation.ErrorRecord: 19621801 exception =
System.Runtime.InteropServices.COMException (0x800706BA): The RPC
server is unavailable. (Exception from HRESULT: 0x800706BA)
   at
System.Runtime.InteropServices.Marshal.ThrowExceptionForHRInternal(Int32 errorCode, IntPtr errorInfo)
   at System.Management.ManagementScope.InitializeGuts(Object o)
   at System.Management.ManagementScope.Initialize()
   at System.Management.ManagementObjectSearcher.Initialize()
   at System.Management.ManagementObjectSearcher.Get()
   at Microsoft.PowerShell.Commands.GetWmiObjectCommand.BeginProcessing()
errorId = GetWMICOMException errorCategory = InvalidOperation
targetObject =
DEBUG: ErrorRecord Information: 0 :  Constructor Leave Ctor
System.Management.Automation.ErrorRecord: 19621801

A work around for your code could be:

try
{
    $colItems = get-wmiobject -class "Win32_PhysicalMemory" -namespace "root\CIMV2" -computername $strComputerName -Credential $credentials
    if ($?)
    {
      foreach ($objItem in $colItems) 
      {
          write-host "Bank Label: " $objItem.BankLabel
          write-host "Capacity: " ($objItem.Capacity / 1024 / 1024)
          write-host "Caption: " $objItem.Caption
          write-host "Creation Class Name: " $objItem.CreationClassName      
          write-host
      }
    }
    else
    {
       throw $error[0].Exception
    }